Structural Panels for Exposed Surfaces

ABSTRACT

A method includes determining a target acoustic profile based on acoustic conditions at an exterior surface exposed to weather. The method further includes determining a plurality of foam layer characteristics based on the target acoustic profile. The method further includes determining one or more of elastomer characteristics based on the target acoustic profile and the plurality of foam layer characteristics. The method further includes providing a foam layer comprising the plurality of foam layer characteristics. The method further includes depositing an elastomer into the provided foam layer according to the one or more elastomer characteristics. The method further includes coupling the foam layer comprising the deposited elastomer onto the exterior surface exposed to weather. The foam layer including the deposited elastomer absorbs acoustic energy corresponding to the target acoustic profile.

TECHNICAL FIELD

This disclosure relates in general to structural panels, and moreparticularly to structural panels for exposed surfaces.

BACKGROUND

Aircraft are subject to a number of environmental conditions, such asice buildup and external noise, that may be detrimental to the aircraft,cargo, and passengers. Ice buildup on aircraft wings is a well-knownproblem that plagues both the military and civilian aerospace industry.When the ice reaches a critical mass that exceeds the adhesion strengthsof the sheets, it releases with little warning and may impact the sideof the fuselage and cause damage.

SUMMARY OF THE DISCLOSURE

According to one embodiment, an apparatus includes a foam layer, acoating layer and an elastomer. The foam layer includes a first surfacefor coupling the apparatus to a surface exposed to weather, a secondsurface opposite the first surface, and a plurality of pores within thefoam layer. The coating layer is deposited on the second surface of thefoam layer. The elastomer is deposited within the plurality of poreswithin the foam layer.

According to another embodiment, a method includes depositing anelastomer within a plurality of pores of a foam panel. The foam panelincludes a first surface for coupling the foam panel to a surfaceexposed to weather, a second surface opposite the first surface, and aplurality of pores within the foam layer. The method further includescoating the second surface of the foam panel with a coating layer. Themethod also includes coupling the foam panel to the surface exposed toweather.

According to yet another embodiment, a method includes determining atarget acoustic profile based on acoustic conditions at an exteriorsurface exposed to weather. The method further includes determining aplurality of foam layer characteristics based on the target acousticprofile. The method further includes determining one or more ofelastomer characteristics based on the target acoustic profile and theplurality of foam layer characteristics. The method further includesproviding a foam layer comprising the plurality of foam layercharacteristics. The method further includes depositing an elastomerinto the provided foam layer according to the one or more elastomercharacteristics. The method further includes coupling the foam layercomprising the deposited elastomer onto the exterior surface exposed toweather. The foam layer including the deposited elastomer absorbsacoustic energy corresponding to the target acoustic profile.

The present disclosure may provide numerous advantages. For example, thefoam layer combined with the elastomer may be sufficiently strong andelastic to absorb impacts from objects, thereby protecting the surfaceon which the apparatus is coupled. Absorption of mechanical energy maybe tailored based on the materials used in the foam panel and/or theelastomer deposited within the foam panel. As another example, the foampanel may comprise a metallic foam having a neutral or negativePoisson's ratio. Having a neutral or negative Poisson's ratio mayenhance adhesion of the foam panel and certain absorption properties.Another advantage of the present disclosure is that the coating layer incombination with the foam layer may be hydrophobic. The hydrophobicnature of the apparatus may prevent the buildup of ice on the surface ofthe apparatus and thereby, the surface exposed to weather. As yetanother example, the apparatus may exhibit nonlinear mechanicalabsorption capabilities, which may serve as a shrapnel barrier orlow-grade ballistics armor. Certain other advantages may be realizedwith the use of fluorinated elastomer material deposited within the foamlayer. For example, fluorinated elastomers may be more resistant todegradation and other environmental forces.

Other aspects disclosed herein provide other advantages. For example,using a target acoustic profile, a foam layer with a deposited elastomermay be produced to absorb acoustic energy based on the target acousticprofile. Selective acoustic energy absorption may enhance the safety andcomfort of passengers in vehicles such as an aircraft. As anotherexample, certain foam layer and elastomer characteristics may bedetermined based on the acoustic profile. By choosing the set ofcharacteristics that provide the panel with acoustic absorption mostclosely matching the acoustic profile, the foam layer with depositedelastomer may be optimized for particular exterior surfaces andconditions. As yet another example, an additional foam layer may beadded to the foam layer with deposited elastomer to improve theabsorption characteristics in the created panel. The additional foamlayer may be disposed between the exterior surface and the foam layer,protecting the additional foam layer from environmental conditions.

Other technical advantages will be readily apparent to one skilled inthe art from the following figures, descriptions, and claims. Moreover,while specific advantages have been enumerated above, variousembodiments may include all, some, or none of the enumerated advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description, taken inconjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating an example aircraft on which a one ormore panels may be coupled to an exterior surface, according to certainembodiments;

FIG. 2 is a cross-sectional view illustrating an example of the panel ofFIG. 1, according to certain embodiments;

FIG. 3 is a flow chart diagram illustrating an example method ofcoupling a panel to a surface exposed to weather, according to certainembodiments;

FIG. 4 is an example absorption plot of acoustic energy over a frequencyrange; and

FIG. 5 is a flow chart diagram illustrating an example method ofproviding a panel with selective acoustic energy absorptioncharacteristics, according to certain embodiments.

DETAILED DESCRIPTION OF THE DISCLOSURE

To facilitate a better understanding of the present disclosure, thefollowing examples of certain embodiments are given. The followingexamples are not to be read to limit or define the scope of thedisclosure. Embodiments of the present disclosure and its advantages arebest understood by referring to FIGS. 1 through 5, where like numbersare used to indicate like and corresponding parts.

Ice may build up on the wings or other parts of an aircraft duringoperation. If allowed to build up, the ice on the aircraft may reach acritical mass such that the weight of the sheet of ice exceeds theadhesion strength of the ice. The ice sheets may then release from theaircraft and impact a portion of the aircraft, such as the fuselage,potentially causing damage.

The amount of ice allowed to build up on parts of an aircraft may belimited by embedded heaters. Heated laminate or wires embedded into acoating may supply heat to melt the ice, preventing its buildup. Thewires and heaters, however, require maintenance, and often cause coatingfailures due to the highly localized temperatures at the surface of theaircraft.

External noise reduction on aircraft, targeting low frequencies, may beachieved by using high volume polyurethane foam. This foam, however,easily degrades during regular operation of the aircraft. The foam hasto be replaced regularly, increasing material and maintenance costs.

To address these and other problems, embodiments of the disclosureprovide structural panels that may be adhered to exposed surfaces suchas the exterior of an aircraft. Certain structural panels adhered toportions of an aircraft may allow the aircraft to avoid damage fromimpinging ice and may reduce acoustic energy. For example, a foam panelmay include a super hydrophobic coating layer and elastomer depositedwithin the foam. A low-density, high-strength foam may enable the panelsto absorb mechanical energy from ice impact. A coating layer may preventice buildup and serve as a UV tolerant rain erosion topcoat. Thedeposited elastomers may mechanically reinforce the foam and provideacoustic dampening properties.

Additionally, foam panels may be created with selective acousticreduction properties. For example, foam panels may be constructed toabsorb particular frequencies at certain levels of absorption. A targetacoustic profile may first be determined based on the surroundingenvironment of the target surface. Using the target acoustic profile,the foam panel may be constructed by first determining foam layercharacteristics and elastomer characteristics that will enhance theabsorption of the targeted acoustic energy. Additional foam layers maybe added to change the absorption characteristics of the foam panel tobetter absorb acoustic energy based on the acoustic profile. By creatingacoustic energy selective foam panels, the harmful or undesirableacoustic energy may be reduced more effectively. When attached to theexterior of an aircraft, such panels may reduce the amount of noiseinside the fuselage, thereby increasing the comfort and safety of anypassengers.

Accordingly, aspects of the present disclosure include an apparatusthat, in one embodiment, includes a foam layer, a coating layer and anelastomer. The foam layer includes a first surface for coupling theapparatus to a surface exposed to weather, a second surface opposite thefirst surface, and a plurality of pores within the foam layer. Thecoating layer is deposited on the second surface of the foam layer. Theelastomer is deposited within the plurality of pores within the foamlayer.

In additional aspects, the present disclosure includes a method that, inone embodiment, includes determining a target acoustic profile based onacoustic conditions at an exterior surface exposed to weather. Themethod further includes determining a plurality of foam layercharacteristics based on the target acoustic profile. The method furtherincludes determining one or more elastomer characteristics based on thetarget acoustic profile and the plurality of foam layer characteristics.The method further includes providing a foam layer comprising the one ormore foam layer characteristics. The method further includes depositingan elastomer into the provided foam layer according to the one or moreelastomer characteristics. The method further includes coupling the foamlayer comprising the deposited elastomer onto the exterior surfaceexposed to weather. The foam layer including the deposited elastomerabsorbs acoustic energy corresponding to the target acoustic profile.

The present disclosure may provide numerous advantages. For example, thefoam layer combined with the elastomer may be sufficiently strong andelastic to absorb impacts from objects such as ice, thereby protectingthe surface on which the apparatus is coupled. Absorption of mechanicalenergy may be tailored based on the materials used in the foam paneland/or the elastomer deposited within the foam panel. As anotherexample, the foam panel may comprise a metallic foam having a neutral ornegative Poisson's ratio. Having a neutral or negative Poisson's ratiomay enhance adhesion of the foam panel and certain absorptionproperties. Another advantage of the present disclosure is that thecoating layer in combination with the foam layer may be hydrophobic. Thehydrophobic nature of the apparatus may prevent the buildup of ice onthe surface of the apparatus and thereby, the surface exposed toweather. As yet another example, the apparatus may exhibit nonlinearmechanical absorption capabilities, which may serve as a shrapnelbarrier or low-grade ballistics armor. Certain other advantages may berealized with the use of fluorinated elastomer material deposited withinthe foam layer. For example, fluorinated elastomers may be moreresistant to degradation and other environmental forces.

Other aspects disclosed herein provide other advantages. For example,using a target acoustic profile, a foam layer with a deposited elastomermay be produced to absorb acoustic energy based on the target acousticprofile. Selective acoustic energy absorption may enhance the safety andcomfort of passengers in vehicles, such as an aircraft. As anotherexample, certain foam layer and elastomer characteristics may bedetermined based on the acoustic profile. By choosing the set ofcharacteristics that provide the panel with acoustic absorption mostclosely matching the acoustic profile, the foam layer with depositedelastomer may be optimized for particular exterior surfaces andconditions. As yet another example, an additional foam layer may beadded to the foam layer with deposited elastomer to improve theabsorption characteristics in the created panel. The additional foamlayer may be disposed between the exterior surface and the foam layer,protecting the additional foam layer from the environmental conditions.

Other technical advantages will be readily apparent to one skilled inthe art from the following figures, descriptions, and claims. Moreover,while specific advantages have been enumerated above, variousembodiments may include all, some, or none of the enumerated advantages.

Additional details are discussed in FIGS. 1 through 5. FIG. 1illustrates an example aircraft on which one or more panels may becoupled, and FIG. 2 shows a cross-sectional view of an example of thepanel of FIG. 1. FIG. 3 illustrates an example method of coupling apanel to an exposed surface. FIG. 4 illustrates an example absorptionplot of the absorption coefficient plotted over a range of frequencies.FIG. 5 is a flow chart diagram illustrating an example method ofproviding a panel with selective acoustic energy absorptioncharacteristics.

FIG. 1 is a diagram illustrating an example aircraft on which one ormore panels may be coupled to an exterior surface, according to certainembodiments. Aircraft 100 may be any type of airborne vehicle in anembodiment. Aircraft 100 may include a fuselage 110, wings 120, and oneor more panels 130 coupled to aircraft 100 in certain embodiments.

In particular embodiments, aircraft 100 may include a verticalstabilizer 140 and horizontal stabilizers 150. In other embodiments,aircraft 100 may be a tailless aircraft. In some embodiments, aircraft100 may be a manned aircraft and may include one or more passengers. Inother embodiments, aircraft 100 may be an unmanned aerial vehicle (UAV).

Fuselage 110 may be a structural component of aircraft 100 in anembodiment. Fuselage 110 may be any shape. Fuselage 110 may beconfigured to hold crew, passengers, or cargo, in some embodiments.Fuselage 110 may be coupled to wings 120 in certain embodiments. In someembodiments, fuselage 110 is also coupled to one or more of verticalstabilizer 140 and horizontal stabilizers 150.

Aircraft 100 may have an exterior surface 160 exposed to weather.Exterior surface 160 may be subject to wind, rain, snow, ice, noise orother environmental conditions during operation, including while theaircraft 100 is airborne. Exterior surface 160 may extend to the surfaceof one or more of fuselage 110, wings 120, vertical stabilizer 140, andhorizontal stabilizers 150.

One or more panels 130 may be coupled to any suitable portion ofexterior surface 160 of aircraft 100. For example, panels 130 may becoupled to one or more of fuselage 110, wings 120, vertical stabilizer140, and horizontal stabilizers 150. In some embodiments, multiplepanels 130 may be coupled to a particular portion of aircraft 100. Forexample, two panels 130 may be coupled to exterior surface 160 ofaircraft 100 at fuselage 110.

In some embodiments, panels 130 may protect aircraft 100 from releasedice or other projectiles. For example, ice may form on wings 120 ofaircraft 100 during flight. After reaching a critical mass, the ice mayrelease from wings 120 and impinge aircraft 100 at fuselage 110, wings120, vertical stabilizer 140, or horizontal stabilizers 150. Panels 130coupled to aircraft 100 may deflect the released ice and absorb theenergy from the impact, thereby protecting aircraft 100. In anotherexample, panels 130 may act as a cladding having non-linear mechanicalenergy absorption capabilities, which may serve as a shrapnel barrier ora low grade ballistics armor for aircraft 100.

Panels 130 may also protect aircraft 100, and any passengers or cargo,from acoustic disturbance or damage. For example, panels 130 may absorbacoustic energy that is detrimental to aircraft 100 and/or itspassengers and cargo. As a specific example, panels 130 may absorbacoustic energy generated by one or more engines of aircraft 100.

FIG. 2 is a cross-sectional view illustrating an example panel 130 thatmay be coupled to a surface exposed to weather 210, according to certainembodiments. In particular embodiments, panel 130 includes a foam layer131, a coating layer 132, and an elastomer 133. Foam layer 131 includesa first surface 134, a second surface 135 opposite first surface 134,and a plurality of pores 136 within foam layer 131. Coating layer 132 isdeposited on second surface 135 of foam layer 131. Elastomer 133 isdeposited within pores 136 of foam layer 131.

Foam layer 131 may comprise any suitable foam material. In particularembodiments, foam layer 131 comprises a metallic foam, a ceramic foam,or a vitreous carbon foam. For example, foam layer 131 may comprise aporous metallic foam made out of certain metals, such as aluminum,copper, or nickel. A metallic foam may comprise one or more metals inorder to provide the desired properties of foam layer 131 and panel 130.As an example, foam layer 131 may be a layer of porous aluminum which isapproximately 80% air. Not only is the porous aluminum extremelylightweight, the pores within the foam may also provide thermalinsulation.

In particular embodiments, foam layer 131 comprises ceramic foam. Forexample, foam layer 131 is a ceramic foam including aluminum. In anotherexample, the ceramic foam includes titanium oxide. In yet anotherexample, foam layer 131 includes ceramic foam that is a carbide ceramic.In particular embodiments, foam layer 131 comprises a vitreous carbonfoam. The vitreous carbon foam may be derived from pyrolized polymers.

In general, the foam material in foam layer 131 allows foam panel 130 toabsorb mechanical energy, such as energy from an impact from an object.An object impacting panel 130 may cause foam layer 131 to compress,distributing the impact over a large area of panel 130 over a longerperiod of time. For example, a sheet of ice dislodged from wing 120 ofaircraft 100 may impact panel 130 adhered to fuselage 110 of aircraft100. The impact from the ice sheet compresses foam layer 131, whichdistributes the force of the impact over a longer period of time byincreasing the impact time, and over a larger area of panel 130. In thismanner, foam layer 131 of panel 130 may protect portions of aircraft100, or other surfaces, such as roofs and exterior walls of a building,from damaging impacts through mechanical energy absorption.

Different foam compositions may provide different advantages in certainapplications. In certain embodiments, certain metallic foams, such asnickel and aluminum, may have non-linear mechanical energy absorptioncapabilities. Metallic foams, therefore, not only may reduce damage fromice impacts, but may also serve as shrapnel barriers or low gradeballistics armor. Protection from shrapnel or ballistics provided bymetallic foams in panel 130 at a lower weight cost compared tonon-porous cladding conventionally used.

In addition, metallic foam may be post-processed to tailor itsmechanical properties. For example, the foam's Poisson ratio may bealtered during this post processing. In particular embodiments, themetallic foam may comprise a neutral (e.g. approximately 0) or negativePoisson's ratio.

In general, the Poisson's ratio is the signed ratio of transverse strainto axial strain. In other words, Poisson's ratio represents the ratio ofa material's expansion in directions perpendicular to an appliedcompression of the material. Typically, materials exhibit a positivePoisson's ratio. That is, materials expand in directions orthogonal tothe compression direction. In some cases, materials may be processed tochange their Poisson's ratio. In certain embodiments, a neutral ornegative Poisson's ratio may be provided.

Materials having a neutral or negative Poisson's ratio may providedesirable properties for panel 130. For example, the lower the Poisson'sratio, the less expansion in directions perpendicular to the compressiondirection. Less expansion may improve adhesion between panel 130 tosurface exposed to weather 210. The reduced expansion helps foam layer131 retain its shape despite compression due to impact energyabsorption. As another example, the Poisson's ratio may determine amaterial's mechanical absorption characteristics. Providing a neutral ornegative Poisson's ratio may enhance the mechanical absorptioncharacteristics of foam layer 131 enabling more energy absorption ortailoring the absorption characteristics to particular types of impacts.For example, tailored foams having non-linear mechanical energyabsorption capabilities may be useful as shrapnel barrier or low gradeballistics armor.

Different processes may be used to provide a material with a neutral ornegative Poisson's ratio. As one example, metallic foam may beplastically deformed to change the structure of the metallic foam inorder to provide a neutral or negative Poisson's ratio. Persons havingordinary skill in the art would recognize that any suitable method toprovide a material with a neutral or negative Poisson's ratio may beemployed.

Ceramic and carbon foams may provide advantages different from or inaddition to those advantages of metallic foams. Ceramic and carbon foamsmay be processed in order to provide resistance to high temperatures.For example, certain high temperature elastomers may be applied to theceramic or carbon foam in order protect the foam from high temperatures.In certain embodiments, the ceramic or carbon foams are resistant totemperatures exceeding 450 degrees Fahrenheit. In this manner, panels130 may be placed in high temperature regions. As an example, certainportions of aircraft 100 may be subject to high temperatures,particularly near engines and/or exhaust areas. Panels 130 havingceramic or carbon foam processed with high temperature elastomers may beplaced in high temperature areas and protect the surfaces from impactsand reduce acoustic energy.

In some embodiments, multiple panels 130 may be coupled to surfaceexposed to weather 210. Each panel 130 may have differentcharacteristics chosen for the different portions of surface exposed toweather 210 on which each panel 130 is coupled. For example, foam layer131 of a first panel 130 may be treated with high temperatureelastomers, if it is to be coupled to a portion of surface exposed toweather 210 subject to high temperatures (e.g., a portion of exteriorsurface 160 near an engine of aircraft 100). In other embodiments, foamlayer 131 of a second panel 130 may include a metallic foam which hasnon-linear mechanical energy absorption properties best suited toprotect that portion of surface exposed to weather 210. In addition todifferences in the types of foam used in foam layer 131, panels 130 maybe tailored to particular applications based on elastomer 133 depositedin a plurality of pores in foam layer 131, as described in more detailbelow.

Foam layer 131 includes a plurality of pores 136 within foam layer 131.The porous nature of foam layer 131 provides several advantages. First,as alluded to above, pores 136 reduce the density, and thus the weight,of foam layer 131 and panel 130. The weight carried by a vehicle mayimpact fuel consumption and other operating considerations. This may beespecially relevant for aircraft, where fuel is costly and refueling iscarefully planned to minimize carrying weight.

In some embodiments, pores 136 within foam layer 131 may be filled withother materials, such as elastomer 133. As will be discussed in moredetail below, elastomer 133 may enhance certain properties of panel 130,including mechanically reinforcing foam layer 131 and optimizingacoustic energy reduction.

While certain foams used in foam layer 131 exhibit mechanical absorptionproperties, such properties may be enhanced by introducing one or moreelastomers 133 into a portion of pores 136 in foam layer 131. Elastomer133 deposited within pores 136 may have a certain elasticity which mayhelp foam layer 131 resist impacts and absorb energy more effectively.The types of elastomer 133 deposited within pores 136 of foam panel 131may differ based on the particular application. For example, a firsttype of elastomer 133 may be chosen if panel 130 is used on fuselage 110of aircraft 100, whereas a second type of elastomer 133 may be used ifpanel 130 is coupled to surface exposed to weather 210 that is subjectto high temperatures.

In addition to providing mechanical reinforcement of foam layer 131,elastomer 133 may provide acoustic energy reduction characteristics topanel 130. In some embodiments, elastomer 133 is chosen to reduce theacoustic energy at a particular frequency or band of frequencies. Inorder to target particular frequencies, one or more of the typeelastomer 133, the type of foam used in foam layer 131, the pore densityof foam layer 131, and the saturation of elastomer 133 in foam layer 131may be adjusted or considered. The optimal parameters may be dictated bythe targeted application. For example, for panels 130 on fuselage 110 ofaircraft 100 near propellers, elastomer 133 may be chosen and depositedsuch that panel 130 absorbs acoustic energy at low frequencies at a highabsorption coefficient.

In particular embodiments, elastomer 133 is a fluorinated elastomer(also described as a fluoroelastomer). Fluorinated elastomer, as used inthis disclosure, may refer to any material categorized under the “FKM”fluoroelastomer category according to the American standard ASTM.Fluorinated elastomers may provide certain advantages when applied tofoam layer 131 in panels 130. For example, fluorinated elastomers may bemore durable than other elastomers and more resistant to environmentalconditions and chemicals. Additionally, certain fluorinated elastomersmay provide acoustic reduction at particular frequencies. For example, afluorinated elastomer deposited within foam layer 131 may absorbacoustic energy at lower frequencies, such as energy from sounds frompropeller engines, for example.

In particular embodiments, a second elastomer 133 may be depositedwithin pores 136 within foam layer 131. The combination of a firstelastomer 133 with a second elastomer 133 may enhance desiredproperties, such as mechanical and acoustic energy absorption. Thecombination of multiple elastomers 133 may require particular depositionprocedures and/or curing techniques as understood by those having skillin the art. In some embodiments, more than two elastomers may bedeposited within pores 136 of foam panel 131. For example, a thirdelastomer 133 may be deposited in addition to two other elastomers 133.The relative quantities of the elastomers 133 may be tailored based onone or more of the foam in foam layer 131, the type of exposed surfaceonto which the panel 130 is coupled, and the environmental conditions ofthe exposed surface.

In some embodiments, panel 130 includes a coating layer 132 deposited onsecond surface 135 of foam layer 131. Coating layer 132 may be depositedon second surface 135 of panel 130 that is directly exposed to weather.Exposure to weather may include exposure to rain, ice, snow, noise,wind, sun, or any other environmental conditions. As discussedpreviously, impacts from ice sheets that are released from portions ofaircraft 100 may cause damage to exterior surface 160. Panel 130 may notonly be constructed to absorb energy from such impacts, but also preventthem from occurring. For example, coating layer 132 (and optionally foamlayer 131) may include materials or chemicals which limit ice adhesionby reducing the surface energy. Surfaces with lower surface energy mayresult in larger contact angles between the surface and a liquid, suchas water. These angles may represent the cohesion between the surfaceand the liquid, where a higher angle represents a lower cohesion (i.e.,less energetically favorable to wet the surface).

In some embodiments, coating layer 132 may include materials whichrelease ice sheets formed on the surface of coating layer 132 beforeaccumulating to a dangerous thickness or size. In particularembodiments, coating layer 132 includes materials which help prevent icefrom forming at the surface. In particular embodiments, coating layer132 is a superhydrophobic fluorinated coating. In some embodimentscoating layer 132 may include one or more elastomer coatings at variousconcentrations to optimize properties of coating layer 132 that limitice adhesion.

In particular embodiments, coating layer 132 may serve as a rain erosiontopcoat. Various aircraft, both military and commercial, requireprotection from water impacting the surface at speeds of up to 400 knotsor more. Water droplets may strip off various coatings on aircraft,requiring maintenance and reapplication. A rain erosion topcoat may beapplied in order to protect against the erosion of coatings or materialsunderneath the rain erosion topcoat. In this manner, coating layer 132may also serve as a rain erosion topcoat, protecting the other layers ofpanel 130 and the surface exposed to weather 210.

In particular embodiments, coating layer 132 may be UV tolerant.Ultraviolet radiation may damage certain portions of panel 130 and/orsurface exposed to weather 210. For example, many natural and syntheticpolymers may degrade when exposed to UV radiation. Degradation inmaterials in panel 130 may lead to structural failure or diminishedmechanical or acoustic energy absorption. For example, UV radiation maydegrade elastomer 133 such that impacts from ice sheets cause panel 130to crack or separate from surface exposed to weather 210. In thismanner, coating layer 132 may protect panel 130 and surface exposed toweather 210 from UV radiation.

Coating layer 132 may have one or more of the advantageous propertiesdiscussed above. For example, coating layer 132 may include materialswhich together prevent rain erosion, UV degradation, and limit iceadhesion. In other embodiments, panel 130 may comprise additionalcoating layers which provide one or more of these properties. Forexample, a rain erosion topcoat layer may be applied on top of coatinglayer 132.

Panel 130 may be coupled to surface exposed to weather 210 by couplingfirst surface 134 of foam layer 131 to surface exposed to weather 210.In particular embodiments, surface exposed to weather 210 is a surfaceof a vehicle. In some embodiments, the vehicle is aircraft 100, a boat,a rocket, or a space vehicle. For example, surface exposed to weather210 may be exterior surface 160 of aircraft 100, as depicted in FIG. 1.

In certain embodiments, surface exposed to weather 210 may be anexterior surface of a building. In such embodiments, panel 130 mayprotect the building by absorbing mechanical impact caused by rain, ice,hail, sleet or debris, and reducing acoustic energy inside the building.For example, multiple panels 130 may be attached to the exterior of abuilding near factories producing an excess amount of noise that maydisrupt activities within the building.

Panel 130 may be coupled to surface exposed to weather 210 by anysuitable means. In particular embodiments, panel 130 may be coupled tosurface exposed to weather 210 by an epoxy. For example, multiple panels130 may be coupled to exterior surface 160 of aircraft 100 with anepoxy. The means to couple the panels to the target surface may varybased on a variety of factors, such as the composition of foam layer130, the type of surface exposed to weather 210, and conditions to whichthe adhered-to surface is exposed. A person having skill in the artwould recognize that there may be a number of ways to couple the panel130 to surface exposed to weather 160.

FIG. 3 is flow chart diagram illustrating an example method 300 ofcoupling panel 130 to surface exposed to weather 210, according tocertain embodiments.

Method 300 may begin at step 310 where an elastomer such as elastomer133 is deposited within a plurality of pores of a foam panel such asfoam panel 131 or any suitable foam structure. The deposited elastomermay mechanically reinforce the foam panel and provide acoustic energyabsorption. Additionally, the deposited elastomer may enhance thehydrophobic properties of the foam panel. As disclosed above, elastomer133 may be chosen based on the target application of panel 130 based ona variety of factors.

At step 320, a surface such as second surface 135 of foam panel 131 iscoated with a coating layer such as coating layer 132 after theelastomer is deposited within the foam panel in step 310. As describedabove, coating layer 132 may provide certain protections to foam layer131. For example, coating layer 132 may be UV tolerant, serve as a rainerosion topcoat, and/or provide a hydrophobic surface for foam panel131. In particular embodiments, coating layer 132 is a superhydrophobicfluorinated coating.

At step 330, the foam panel of step 320 is coupled to a surface exposedto weather (e.g., exterior surface 160 of aircraft 100 or surfaceexposed to weather 210). The foam panel, which includes the coatinglayer of step 310 and the deposited elastomer of step 310, may becoupled to the surface in any suitable manner. The technique used tocouple the foam panel may depend on one or more of the type of foam inthe foam panel, the type of the surface exposed to weather, and theenvironmental conditions of the surface exposed to weather. Inparticular embodiments, an epoxy may be used to couple the foam panel tothe surface exposed to weather. A certain epoxy may be chosen to ensurethat the foam panel remains coupled to the surface despite surfaceimpacts and the compression of the foam panel. After step 330, method300 may end.

Modifications, additions, or omissions may be made to method 300depicted in FIG. 3. Method 300 may include more, fewer, or other steps.For example, in an optional step 315, the foam panel may be processed toprovide the foam panel with a neutral or negative Poisson's ratio.Having a neutral or negative Poisson's ratio may have certainadvantages, as described above. Furthermore, steps may be performed inparallel or in any suitable order. While various components of panel 130were discussed in relation to the steps in method 300, the steps ofmethod 300 may be taken using any suitable component or combination ofcomponents of panel 130.

FIG. 4 is an example absorption plot 400 that may be used to determinecharacteristics of one or more elements in a structural panel such aspanel 130. As illustrated in FIG. 4, absorption plot 400 plots theabsorption coefficient as a function of the frequency of acousticenergy. In other words, absorption plot 400 illustrates the amount orportion of the acoustic energy absorbed at each frequency. Absorptionplot 400 includes a target peak frequency 405, a target absorptioncoefficient 410, and a target frequency width 415.

In general, absorption plot 400 may also represent a target acousticprofile of an environment. For example, absorption plot 400 may be basedon the acoustic environment of a particular area, surface, or space. Insome embodiments, absorption plot 400 may be based on measurements ofthe acoustic energy at various frequencies at surface exposed to weather210, such as exterior surface 160 of aircraft 100 during operation. Asan example, absorption plot 400 may be generated using measurements ofthe acoustic energy across a frequency at surface exposed to weather210. Using the acoustic energy intensity values across the measuredfrequency range, absorption coefficient values may be determined foreach measured frequency. For example, a higher absorption coefficientvalue may be associated with a higher measured intensity at thatfrequency. Other factors, such as human sensitivity or the type ofsurface exposed to weather, may affect the generation of absorption plot400 based on measured acoustic energy intensities. For example,frequencies outside the normal human hearing range may not beconsidered, or may be associated with a lower or null absorptioncoefficient value. In this manner, absorption plot 400 may represent atarget acoustic profile, which may be used to provide materials orcomponents to produce a structural panel, such as panel 130, that hassimilar acoustic energy absorption characteristics as the targetacoustic profile.

As illustrated in FIG. 4, absorption plot 400 plots a continuous curveover the range of frequencies shown. In some embodiments, absorptionplot 400 is a discontinuous plot or a set of discontinuous pointsextrapolated to provide a continuous plot. In some embodiments,absorption plot 400 is only plotted within a particular frequency rangeor within a particular absorption coefficient range. In someembodiments, absorption plot 400 is not a single curve, but a set ofcurves over the frequency range. For example, there may be a range ofabsorption coefficients for each frequency such that absorption plot 400plots out an area bounded by a bottom curve and a top curve across thefrequency values.

In certain embodiments, absorption plot 400 may represent the absorptioncharacteristics of a material or composite. For example, a plot may begenerated by measuring the absorption by a material of acoustic energyat various frequencies. The absorption plot generated by measuring theabsorption characteristics of a material may be compared to a targetacoustic profile. In this manner, absorption plot 400 may be used toconfirm that chosen characteristics provide the correct or adequateabsorption characteristics desired. Thus, absorption plot 400 may notonly be use as a target acoustic profile, but also as a tool to comparethe characteristics of a produced material to a target acoustic profile.

Target peak frequency 405 is a frequency at which the absorptioncoefficient is maximized. For example, absorption plot 400 shows asingle target peak frequency 405 where the corresponding absorptioncoefficient is largest across the frequencies on plot 400. In someembodiments, absorption plot 400 may have multiple target peakfrequencies 405 and the absorption coefficients at those target peakfrequencies 405 may be only local maximums, e.g. one peak may be largerthan the other, but each locally maximizes the absorption coefficient.For example, a twin peak absorption plot of the absorption coefficientsfor a certain material may have a low frequency peak and a highfrequency peak.

Target absorption coefficient 410 is a value for the coefficient ofabsorption at a particular frequency. In general, the coefficient ofabsorption is a measurement of how much acoustic energy is absorbed at aparticular frequency. In certain embodiments, a particular value fortarget absorption coefficient 410 is chosen for target peak frequency405. For example, it may be desirable for a material or composite tohave an absorption coefficient above 0.90 at a particular target peakfrequency 405. In this manner, a material may be chosen which has acoefficient of absorption at least as large as target absorptioncoefficient 410 at target peak frequency 405. the chosen materialabsorbs most of the acoustic energy at the particular frequency.

Target frequency width 415 is a width between the highest frequency andlowest frequency having an absorption coefficient above a particularvalue. For example, target frequency width 415 on absorption plot 400 isthe frequency width at an absorption coefficient labeled al. In certainembodiments, a material is chosen having a frequency width at least aslarge as target frequency width 415 around target peak frequency 405.For example, if target peak frequency 405 has a value of 400 Hz, it maybe desirable to have a material with a frequency width at least as largeas target frequency width 415 of 100 Hz. The frequency range aroundtarget peak frequency 405 may be symmetric, or alternatively,asymmetric. Since target frequency width 415 is dependent on a thresholdabsorption coefficient value, a threshold value and target frequencywidth 415 may be utilized when determining the appropriate material(s).Using the example above, if an absorption coefficient of 0.90 at targetparticular peak frequency 405 is chosen, a 100 Hz target frequency width415 at absorption coefficient value of 0.85 may also be chosen. As aresult, a material or composite matching the target acoustic profilecharacteristics will have an absorption coefficient above 0.85 withinthat 100 Hz band and an absorption coefficient of at least 0.90 at thespecified peak frequency.

FIG. 4 merely serves as an illustration to provide context for aspectsin this disclosure. Each surface exposed to weather or material may havea different corresponding absorption plot. For example, the absorptionplot corresponding to a particular surface or material may havedifferent peak frequencies, including having more than one peakfrequency, and have a different shape, including different frequencywidths at various absorption coefficient values. Because of thevariability of the absorption plots, a particular material or compositeof materials may be chosen to target absorption of different acousticenergy profiles. Moreover, a particular material or composite may betailored in order to best absorb acoustic energy at certain levels attargeted frequency ranges.

FIG. 5 is a flow chart diagram illustrating an example method 500 ofproviding a panel with selective acoustic energy absorptioncharacteristics, according to certain embodiments. Method 500 begins instep 502, where a target acoustic profile is determined. The targetacoustic profile may include a set of frequencies, frequency bands, andassociated absorption levels at those frequencies. For example, thetarget acoustic profile may correspond to the acoustic environment, e.g.the levels of acoustic energy across a range of frequencies, at or neara surface exposed to weather. As a specific example, the target acousticprofile may be an absorption plot, such as absorption plot 400,generated based on the acoustic energy profile of exterior surface 160of aircraft 100 near fuselage 110.

In particular embodiments, the exterior surface exposed to weather is anexterior surface of a vehicle, such as exterior surface 160 of aircraft100. Vehicles are often exposed to high intensities of acoustic energynear their exterior surfaces due to the turbulence of the fluidsurrounding the vehicles. High speed vehicles are especially susceptibleto this phenomenon due to their high rate of speed through a fluid, e.g.air or water. The acoustic profile may be based on the acousticconditions of the vehicle during operation. As a particular example, thetarget acoustic profile may correspond to the acoustic energy profilenear a surface of an aircraft during operation. In certain embodiments,the vehicle is one of a boat, an aircraft, an automobile, and a rocket.Each vehicle may be subject to different acoustic conditions. Theacoustic profile may be individually tailored to a particular vehicle ora type or class of vehicle. For example, a rocket and an automobile aresubject to very different acoustic conditions during their operation,but each may benefit from the reduction of that acoustic energy.

In particular embodiments, the acoustic profile is based on humansensitivity to acoustic energy near the surface exposed to weather. Theacoustic profile may be determined in step 502 by focusing onfrequencies affecting humans. For example, certain frequencies ofacoustic energy above or below range of frequencies heard by humans, orotherwise do not affect humans adversely may be neglected or removedfrom consideration when the acoustic profile is determined in step 502.In certain embodiments, the acoustic profile is based on additionalconsiderations, including resonance frequencies of the surface exposedto weather and vibrational sensitivities of objects, structures, orpersons near the surface exposed to weather.

In particular embodiments, the acoustic profile includes target peakfrequency 405, target absorption coefficient 410, and target frequencywidth 415. For example, acoustic energy with high intensity at aparticular frequency may be determined to be target peak frequency 405of the acoustic profile to maximize the absorbed acoustic energy. Sinceit may be desirable to absorb acoustic energy across a range offrequencies, a frequency centered around the frequencies with thehighest intensity levels may be selected as target peak frequency 405.In some embodiments, target peak frequency 405 may be shifted away fromthe frequency with the highest intensity level to account for humansensitivity or other considerations. As another example, target peakfrequency 405 may be determined in order provide the most overallabsorption of acoustic energy. In this manner, even if a material doesnot have a peak absorption coefficient matching target peak frequency405, it may still absorb the most acoustic energy at or near the targetenvironment, e.g. surface exposed to weather 210.

In some embodiments, target absorption coefficient 410 of the acousticprofile may be determined for one or more frequencies. As an example,target absorption coefficient 410 may be selected as a threshold for theabsorption coefficient at one or more of target peak frequency 405 andthe range of frequencies within the target frequency width 415 aroundtarget peak frequency 405. Target frequency width 415 may be determinedat a particular absorption coefficient to provide a minimum absorptioncoefficient across that range of frequencies. In this manner, theacoustic profile may include several characteristics which may be usedto create target absorption plot or a range of target absorption plots,such as absorption plot 400. The target acoustic profile may be used infurther steps in order to provide optimal absorption of acoustic energymatching the target acoustic profile at an exterior surface exposed toweather.

Using the determined target acoustic profile, a plurality of foam layercharacteristics are determined in step 504. The foam layercharacteristics may be determined to aid in selecting an optimal foamlayer to absorb acoustic energy based on the acoustic profile of step502. In certain embodiments, the plurality of foam layer characteristicsincludes a foam layer material, a foam layer pore density, and a foamlayer thickness. Different foam layer materials may absorb acousticenergy at different absorption coefficients across a range offrequencies. Furthermore, different foam layer materials may allowdifferent elastomers to be deposited within the pores of the foam layer.For example, certain high temperature elastomers may only be applied tomaterials that may survive high temperature environments. In certainembodiments, the foam layer material is one of a metallic foam, aceramic foam, or a vitreous carbon foam. As discussed previously,different types of foam materials may have different properties andapplications. This applies equally to their acoustic properties. Thus,depending on the acoustic profile, different foam layer materials may beused.

The foam layer pore density is the density of pores within the foamlayer. Generally, the greater the pore density, the greater the acousticabsorption. High pore densities, however, may reduce the resilience ofthe foam layer against impacts or other damaging events. Thus, the poredensity may be chosen in light of mechanic properties in addition to theacoustic properties. In particular embodiments, the pore density ischosen from a predetermined set of values. For example, the pore densitymay be selected from the set of 5, 10, 20, or 40 pores per inch.

The foam layer thickness may also affect the foam layer's acousticproperties. For example, a thicker foam layer may absorb more acousticenergy, but may be susceptible to greater wear and tear due to operatingconditions. For example, a thicker foam layer may present a largerprofile across which air or another fluid has to flow. Additionally, athicker foam layer may be harder to attach or maintain attached to thetarget exterior surface. Thus, the foam layer thickness may bedetermined based on the acoustic profile and in certain embodiments,also based on other functional considerations.

The various foam layer characteristics may be interdependent. In otherwords, optimizing one characteristic based on the acoustic profile mayreduce the overall effectiveness of the foam layer in absorbing theacoustic energy according to the acoustic profile. In certainembodiments, the determination of the plurality of foam layercharacteristics takes in to account the various interdependencies inorder to best choose the various characteristics for the foam layer.

Using the determined target acoustic profile and the determined foamlayer characteristics, one or more elastomer characteristics aredetermined in step 506. Different types of elastomers may change theacoustic properties of the foam layer to better match different acousticprofiles. Furthermore, different saturation levels of the elastomer inthe foam layer may change the acoustic properties in different ways. Forexample, different elastomer types and saturation levels may shift thepeak absorption frequency or change the frequency width of theabsorption coefficient above a threshold level.

In particular embodiments, the one or more elastomer characteristicsinclude an elastomer composition and an elastomer saturation level. Theelastomer composition could be the designation of one or more types ofelastomers to be deposited in the foam layer. In certain embodiments,the elastomer composition includes an elastomer that is afluoroelastomer. As discussed earlier, fluoroelastomers may beadvantageous for a variety of reasons. Fluoroelastomers may also beuseful in enhancing the foam layer absorption of acoustic energy.

The elastomer saturation represents the saturation level of theelastomer inside the provided foam layer. For example, the elastomersaturation may be a percentage of the space inside the foam layer filledwith the elastomer. As another example, the elastomer saturation may bea weight or volume of the elastomer relative to the provided foam layer.

In particular embodiments, the determined elastomer composition includesmore than one elastomer. For example, step 506 may include substeps ofchoosing first and second elastomers based on the target acousticprofile and the determined foam layer characteristic and thendetermining a ratio between the two elastomers based on the targetacoustic profile, the determined foam layer characteristics, andcharacteristics of the two elastomers. In this manner, the acousticenergy reduction properties may be optimized by mixing two or more typesof elastomers.

In certain embodiments, during one or more of steps 504 and 506, desiredmechanical absorption properties may also be considered when determiningthe foam layer and elastomer characteristics. If the foam layer isintended to be used on a surface subject to impact events, the foamlayer and the elastomer characteristics may be selected to enable thepanel created using the foam layer and elastomer to withstand impacts inaddition to absorbing acoustic energy. For example, certaincharacteristics may be desirable to optimize acoustic energy absorption,but may be detrimental or suboptimal if the intended use also requiresmechanical energy absorption. In this manner, the determination of thecharacteristics for acoustic energy absorption may be constrained by theadditional consideration of mechanical energy absorption.

In step 508, a foam layer is provided with the determined foam layercharacteristics. For example, the determined foam layer characteristicsmay be used to choose a foam layer material with a certain pore densityand layer thickness. Additional steps may be taken to process a foambefore providing the foam layer with the determined foam layercharacteristics. For example, the foam layer may be shaped to a desiredthickness or size, or the foam may be processed to provide it withcertain mechanical properties, such as a certain Poisson's ratio. Incertain embodiments, the foam layer may be chosen from a predeterminedset of foam materials, pore densities, and thickness based on thedetermined foam layer characteristics. A preconfigured foam layer may beprocessed to more closely align it with the determined characteristics.

In step 510, the elastomer is deposited according to the determinedelastomer characteristics. As a result, a foam layer, chosen usingdetermined foam layer characteristics, with deposited elastomer, chosenusing determined elastomer characteristics, may be provided. In thismanner, the foam layer with deposited elastomer may be optimized toabsorb acoustic energy corresponding to the acoustic profile.

In certain embodiments where the elastomer includes more than oneelastomer type or a mixture of different elastomers, step 510 mayinclude substeps of depositing each elastomer into the foam layer. Inother embodiments, the elastomer is deposited in a single process aftertwo or more elastomers are mixed.

In step 512, the foam layer with the deposited elastomer is coupled toan exterior surface exposed to weather. The foam layer may be coupled tothe exterior surface using any suitable techniques. The type of surfaceor the chosen foam layer may determine how the foam layer with thedeposited elastomer is coupled to the surface. In certain embodiments,an epoxy is used to couple the foam layer to the surface.

By coupling the foam layer to the exterior surface, the foam layer withthe deposited elastomer may absorb acoustic energy corresponding to thetarget acoustic profile. Because the target acoustic profile may bebased on the acoustic environment near the exterior surface exposed toweather, the foam layer with the deposited elastomer may absorb a largeportion of the acoustic energy near the exterior surface. In thismanner, acoustic energy absorption may be selectively provided based onthe acoustic conditions of the target surface exposed to weather.

Different exterior surfaces may have different acoustic conditions andcertain embodiments described herein allow for the tailoring of foamlayers with deposited elastomer to target acoustic absorption to thoseconditions. As an example, an aircraft may have a particular acousticenvironment during operation, e.g. during flight or takeoff. By using anacoustic profile based on the specific conditions, the provided foamlayer and deposited elastomer may optimally absorb that acoustic energywhen coupled to an exterior surface of the aircraft. Continuing withthis example, certain embodiments may protect passengers from harmfulnoise and acoustic energy, as well as protect vibrationally sensitiveequipment and reduce dangerous resonance on or near the aircraft.

As an example, method 500 may provide a foam layer for the exteriorsurface of an aircraft. In this example, the target acoustic profile maybe based on the intensity of acoustic energy around the exterior of theaircraft. For example, the exterior surface of a propeller plane may besubject to acoustic energy caused by the propellers in the range from150 to 400 Hz. Alternatively, for jet planes, the acoustic energy maymost intense in the range from 600 Hz to 1.25 kHz.

Continuing with this example, the human sensitivity to particularfrequency ranges may be considered. For example, a peak frequency of 2kHz may be chosen for the target acoustic profile taking into accountthe acoustic energy acoustic energy at the surface and the humansensitivity to specific frequencies. In this example, a targetabsorption coefficient of 0.99 may be chosen for the peak frequency of 2kHz and a target frequency width of 1360 Hz may be chosen to capture therange of 1480 Hz to 2840 kHz. Using these chosen values, the foam layercharacteristics may be determined. In this example, based on the targetacoustic profile, an aluminum foam with 0.5 inch thickness and poredensity of 20 pores per inch may be chosen. Then, based on the acousticprofile and the chosen foam layer, an elastomer may be chosen. In thisexample, a Type 1 FKM fluoroelastomer may be chosen to shift thefrequency attenuation curve of the chosen foam layer to lowerfrequencies. For example, the elastomer may be chosen to only partialfill the foam layer to approximately 50% in order to shift theabsorption attenuation curve such that the attenuation rate is greaterthan 0.99 between 400 Hz to 2 kHz. The chosen foam layer with thedeposited elastomer chosen may be coupled to the exterior of theaircraft in order to provide selective acoustic reduction.

In a variant of the example provided above, the exterior surface of theaircraft may be a high-temperature area, for example near AuxiliaryPower Unites (APU's). In this case, the high temperature atmosphere maybe taken into account. As a result, instead of an aluminum foam, aceramic or carbon foam may be chosen to withstand the exhausttemperatures of up to 1100 degrees Fahrenheit. Additionally, in thisexample, a different fluoroelastomer may be chosen. For example, an FKMtype 2 elastomer may be chosen instead. These examples are providedmerely as instructional examples and a myriad of other embodiments arecontemplated within this disclosure.

In certain embodiments, method 500 may further include steps ofdetermining whether to provide an additional foam layer based on thetarget acoustic profile and coupling the additional foam layer to thefoam layer with the deposited elastomer. Adding an additional foam layermay change the acoustic absorption characteristics of the foam layerwith the deposited elastomer. As an example, an additional foam layermay broaden the absorption peaks of the foam layer with elastomer suchthat a broader range of frequencies are absorbed with a high absorptioncoefficient. Additionally, the additional foam layer may change the peakfrequency absorbed by the foam panel and elastomer.

Furthermore, the foam layer and elastomer may protect the additionalfoam layer from degradation or wear and tear. For example, the foamlayer and elastomer may absorb the impacts from objects, e.g. sheets ofice, which protects the additional foam layer, increasing itsoperational life. In particular embodiments, the additional foam layermay be composed of softer or more fragile materials. In certainembodiments, the additional foam layer is a layer of melamine foam.Melamine foam has well-known acoustic absorption properties, butdegrades quickly, particularly in disruptive environments, such as theexterior of an aircraft during flight. By adding the melamine foam tothe foam layer with deposited elastomer, the acoustic absorptionproperties may be enhanced to provide acoustic absorption properties tobetter match the acoustic profile. At the same time, the melamine foamis protected by the foam layer and elastomer so that it may continue toenhance the acoustic energy absorption throughout the lifetime of thefoam layer.

In certain embodiments, method 500 further includes coating the foamlayer with a superhydrophobic fluorinated coating layer. As discussedpreviously, the coating layer may serve as an rain erosion topcoat layerwhich is UV tolerant. In this manner, the coating layer may help protectthe foam layer from rain erosion and deterioration from exposure to UVradiation.

In certain embodiments, method 500 further includes decoupling a foamlayer from the exterior surface exposed to weather and coupling anotherfoam layer with deposited elastomer onto the exterior surface exposed toweather. In some embodiments, new techniques or materials may be foundthat may be used to create superior foam layers. In this manner,outdated foam layers may be replaced. Thus, in certain embodiments, anold foam layer may be removed and replaced with a new one.

Modifications, additions, or omissions may be made to method 500depicted in FIG. 5. The steps of method 500 may be performed in parallelor in any suitable order. Furthermore, method 500 may include more,fewer, or other steps. The steps of method 500 may be taken using anysuitable component or combination of components, including components ofpanel 130 and/or aircraft 100.

The present disclosure may provide numerous advantages. For example, thefoam layer combined with the elastomer may be sufficiently strong andelastic to absorb impacts from objects, thereby protecting the surfaceon which the apparatus is coupled. Absorption of mechanical energy maybe tailored based on the materials used in the foam panel and/or theelastomer deposited within the foam panel. As another example, the foampanel may comprise a metallic foam having a neutral or negativePoisson's ratio. Having a neutral or negative Poisson's ratio mayenhance adhesion of the foam panel and certain absorption properties.Another advantage of the present disclosure is that the coating layer incombination with the foam layer may be hydrophobic. The hydrophobicnature of the apparatus may prevent the buildup of ice on the surface ofthe apparatus and thereby, the surface exposed to weather. As anotheradvantage, the apparatus may exhibit nonlinear mechanical absorptioncapabilities, which may serve as a shrapnel barrier or low-gradeballistics armor. Certain other advantages may be realized with the useof fluorinated elastomer material deposited within the foam layer. Forexample, fluorinated elastomers may be more resistant to degradation andother environmental forces.

Other aspects disclosed herein provide other advantages. For example,using a target acoustic profile, a foam layer with deposited elastomermay be tailored to absorb acoustic energy based on that acousticprofile. Selective acoustic energy absorption may enhance the safety andcomfort of passengers in vehicles, such as an aircraft. As anotherexample, certain foam layer and elastomer characteristics may bedetermined based on the acoustic profile. By choosing the set ofcharacteristics that provide the panel with acoustic absorption mostclosely matching the acoustic profile, the foam layer with depositedelastomer may be optimized for particular exterior surfaces andconditions. As yet another example, an additional foam layer may beadded to the foam layer with deposited elastomer to improve theabsorption characteristics in the created panel. The additional foamlayer may be disposed between the exterior surface and the first foamlayer, protecting the additional foam layer from environmentalconditions.

Other technical advantages will be readily apparent to one skilled inthe art from the following figures, descriptions, and claims. Moreover,while specific advantages have been enumerated above, variousembodiments may include all, some, or none of the enumerated advantages.

The scope of this disclosure encompasses all changes, substitutions,variations, alterations, and modifications to the example embodimentsdescribed or illustrated herein that a person having ordinary skill inthe art would comprehend. The scope of this disclosure is not limited tothe example embodiments described or illustrated herein. Moreover,although this disclosure describes and illustrates respectiveembodiments herein as including particular components, elements,functions, operations, or steps, any of these embodiments may includeany combination or permutation of any of the components, elements,functions, operations, or steps described or illustrated anywhere hereinthat a person having ordinary skill in the art would comprehend.Furthermore, reference in the appended claims to an apparatus or systemor a component of an apparatus or system being adapted to, arranged to,capable of, configured to, enabled to, operable to, or operative toperform a particular function encompasses that apparatus, system,component, whether or not it or that particular function is activated,turned on, or unlocked, as long as that apparatus, system, or componentis so adapted, arranged, capable, configured, enabled, operable, oroperative.

Although the present disclosure has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present disclosure encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims.

What is claimed is:
 1. A method, comprising: determining a targetacoustic profile, wherein the target acoustic profile is based on anacoustic environment of an exterior surface of an aircraft duringoperation; determining a plurality of metallic foam layercharacteristics based on the target acoustic profile, the plurality ofmetallic foam layer characteristics comprising: a metallic foam layercomposition; a metallic foam layer pore density; and a metallic foamlayer thickness; determining a plurality of elastomer characteristicsbased on the target acoustic profile and the plurality of metallic foamlayer characteristics, the plurality of elastomer characteristicscomprising: an elastomer composition; and an elastomer saturation level;providing a metallic foam layer comprising the plurality of determinedmetallic foam layer characteristics; depositing an elastomer comprisingthe determined elastomer composition into the provided metallic foamlayer at the determined elastomer saturation level; and coupling themetallic foam layer comprising the deposited elastomer onto the exteriorsurface of the aircraft, wherein the metallic foam layer comprising thedeposited elastomer absorbs acoustic energy corresponding to the targetacoustic profile.
 2. The method of claim 1, wherein the target acousticprofile comprises: a target peak frequency; a target absorptioncoefficient; and a target frequency width.
 3. The method of claim 1,further comprising: determining an additional foam layer based on thetarget acoustic profile; and coupling the additional foam layer to themetallic foam layer comprising the deposited elastomer.
 4. The method ofclaim 3, further comprising determining a thickness of the additionalfoam layer based on the target acoustic profile and acousticcharacteristics of the metallic foam layer comprising the depositedelastomer.
 5. The method of claim 3, wherein the additional foam layeris a layer of melamine foam.
 6. The method of claim 1, furthercomprising coating the metallic foam layer with a superhydrophobicfluorinated coating layer on a surface of the metallic foam layeropposite the exterior surface of the aircraft.
 7. The method of claim 1,wherein determining the plurality of metallic foam layer characteristicsand determining the plurality of elastomer characteristics are based ondesired mechanical energy absorption characteristics of the metallicfoam layer comprising the deposited elastomer.
 8. A method, comprising:determining a target acoustic profile based on acoustic conditions at anexterior surface exposed to weather; determining a plurality of foamlayer characteristics based on the target acoustic profile; determiningone or more of elastomer characteristics based on the target acousticprofile and the plurality of foam layer characteristics; providing afoam layer comprising the plurality of more foam layer characteristics;depositing an elastomer into the provided foam layer according to theone or more elastomer characteristics; and coupling the foam layercomprising the deposited elastomer onto the exterior surface exposed toweather, wherein the foam layer comprising the deposited elastomerabsorbs acoustic energy corresponding to the target acoustic profile. 9.The method of claim 8, wherein the plurality of foam layercharacteristics comprises: a foam layer material; a foam layer poredensity; and a foam layer thickness.
 10. The method of claim 9, whereinthe foam layer material is one of a metallic foam, a ceramic foam, or avitreous carbon foam.
 11. The method of claim 8, wherein the one or moreelastomer characteristics are selected from the group consisting of: anelastomer composition; and an elastomer saturation level.
 12. The methodof claim 8, further comprising: determining an additional foam layerbased on the target acoustic profile; and coupling the additional foamlayer to the foam layer comprising the deposited elastomer.
 13. Themethod of claim 8, further comprising coating the foam layer comprisingthe deposited elastomer with a superhydrophobic coating layer on a sideof the foam layer exposed to weather.
 14. The method of claim 8,wherein: the exterior surface exposed to weather is an exterior surfaceof a vehicle; and the vehicle is one of a boat, an aircraft, anautomobile, and a rocket.
 15. The method of claim 8, wherein determiningthe target acoustic profile is based on human sensitivity to acousticenergy near the surface exposed to weather.
 16. The method of claim 8,wherein the elastomer composition comprises at least one elastomer thatis a fluoroelastomer.
 17. The method of claim 8, wherein determining theelastomer composition comprises: choosing a first elastomer based on thetarget acoustic profile and the plurality of foam layer characteristics;choosing a second elastomer based on the target acoustic profile and theplurality of foam layer characteristics; and determining a ratio betweenthe first elastomer and the second elastomer based on the targetacoustic profile, the plurality of foam layer characteristics,characteristics of the first elastomer, and characteristics of thesecond elastomer.
 18. The method of claim 8, further comprising:decoupling the foam layer comprising the deposited elastomer from theexterior surface exposed to weather; and coupling another foam layercomprising a deposited elastomer onto the exterior surface exposed toweather.
 19. A method, comprising: determining a target acoustic profilebased on an acoustic environment of an exterior surface of an aircraftduring operation, the target acoustic profile comprising: a target peakfrequency; a target absorption coefficient; and a target frequencywidth; wherein the target acoustic profile; determining a plurality ofmetallic foam layer characteristics based on the target acousticprofile, the plurality of metallic foam layer characteristicscomprising: a metallic foam layer composition; a metallic foam layerpore density; and a metallic foam layer thickness; determining aplurality of elastomer characteristics based on the target acousticprofile and the metallic foam layer characteristics, the plurality ofelastomer characteristics comprising: an elastomer composition; and anelastomer saturation level; providing a metallic foam layer comprisingthe plurality of determined metallic foam layer characteristics;depositing an elastomer having the determined elastomer composition intothe provided metallic foam layer at the determined elastomer saturationlevel; determining an additional foam layer comprising melamine foambased on the target acoustic profile; coupling the additional foam layerto the metallic foam layer comprising the deposited elastomer; andcoupling the additional foam layer and the metallic foam layercomprising the deposited elastomer onto the exterior surface of theaircraft, wherein the additional foam layer and metallic foam layercomprising the deposited elastomer absorbs acoustic energy correspondingto the target acoustic profile.
 20. The method of claim 19, wherein thetarget peak frequency is within a range of 1480 Hz and 2840 Hz and thetarget absorption coefficient is at least 0.99 at the target peakfrequency.